feat: observe HTTP2 reset and goaway frames

transport/http2/frameObserver.go

@@ -0,0 +1,106 @@
+package http2
+
+import (
+	"crypto/tls"
+	"net"
+	"sync"
+)
+
+const (
+	frameTypeRSTStream byte = 0x3
+	frameTypeGoAway    byte = 0x7
+)
+
+type frameDirection uint8
+
+const (
+	frameRead frameDirection = iota
+	frameWrite
+)
+
+// observedConn keeps the HTTP/2 implementation opaque while exposing the
+// small amount of frame-level telemetry that x/net/http2 does not provide.
+// It parses only the nine-byte frame header and skips payload bytes without
+// buffering them, so large DATA frames cannot increase telemetry memory.
+type observedConn struct {
+	net.Conn
+	onFrame     func(frameDirection, byte)
+	readParser  frameParser
+	writeParser frameParser
+	writeMu     sync.Mutex
+}
+
+func (c *observedConn) Read(buffer []byte) (int, error) {
+	n, err := c.Conn.Read(buffer)
+	if n > 0 {
+		c.readParser.observe(buffer[:n], frameRead, c.onFrame)
+	}
+	return n, err
+}
+
+func (c *observedConn) Write(buffer []byte) (int, error) {
+	c.writeMu.Lock()
+	defer c.writeMu.Unlock()
+	n, err := c.Conn.Write(buffer)
+	if n > 0 {
+		c.writeParser.observe(buffer[:n], frameWrite, c.onFrame)
+	}
+	return n, err
+}
+
+// observedTLSConn preserves the connection state hook used by x/net/http2 so
+// handlers still receive Request.TLS after frame observation is added.
+type observedTLSConn struct {
+	*observedConn
+	state tls.ConnectionState
+}
+
+func (c *observedTLSConn) ConnectionState() tls.ConnectionState { return c.state }
+
+type frameParser struct {
+	prefaceRemain int
+	header        [9]byte
+	headerBytes   int
+	payloadRemain int
+	frameType     byte
+}
+
+func (p *frameParser) observe(buffer []byte, direction frameDirection, onFrame func(frameDirection, byte)) {
+	for len(buffer) > 0 {
+		if p.prefaceRemain > 0 {
+			skip := p.prefaceRemain
+			if skip > len(buffer) {
+				skip = len(buffer)
+			}
+			p.prefaceRemain -= skip
+			buffer = buffer[skip:]
+			continue
+		}
+		if p.payloadRemain > 0 {
+			skip := p.payloadRemain
+			if skip > len(buffer) {
+				skip = len(buffer)
+			}
+			p.payloadRemain -= skip
+			buffer = buffer[skip:]
+			if p.payloadRemain > 0 {
+				continue
+			}
+			onFrame(direction, p.frameType)
+			continue
+		}
+
+		copied := copy(p.header[p.headerBytes:], buffer)
+		p.headerBytes += copied
+		buffer = buffer[copied:]
+		if p.headerBytes < len(p.header) {
+			continue
+		}
+		p.payloadRemain = int(p.header[0])<<16 | int(p.header[1])<<8 | int(p.header[2])
+		p.frameType = p.header[3]
+		p.headerBytes = 0
+		if p.payloadRemain == 0 {
+			onFrame(direction, p.frameType)
+		}
+	}
+}